There are known hollow strain wave gearings which comprise a hollow shaft defining a hollow part that extends through the hollow strain wave gearing along the central-axis direction thereof, and which are configured such that an ellipsoidally contoured wave plug of a wave generator is integrally formed along the outer peripheral surface of the hollow shaft. Patent Document 1 discloses a hollow strain wave gearing comprising a top-hat-shaped flexible externally toothed gear.
In a hollow strain wave gearing of such configuration, both shaft end parts of the hollow shaft are supported by support bearings. The wave generator is configured from the wave plug integrally formed along the outer peripheral surface of the hollow shaft, and a wave bearing fitted on the ellipsoidal outer peripheral surface of the wave plug. The wave bearing comprises inner and outer flexible races capable of flexing along the radial direction.
The wave bearing is mounted in the following manner. A shaft end on one side of the hollow shaft is passed through the wave bearing, and the wave bearing is moved along the outer peripheral surface of the hollow shaft to the wave plug and is mounted on the ellipsoidal outer peripheral surface of the wave plug. The outside diameter of the shaft part extending from the shaft end on one side of the hollow shaft to the wave plug must be made smaller than the inside diameter of the wave bearing. Typically, the outside diameter of the shaft part is made smaller than the minor axis of the ellipsoidal outer peripheral surface of the wave plug to allow the wave bearing to be mounted.